DESCRIPTION (Adapted from applicant's description): Rates of risky behaviors in homeless youths are persistently high, resulting in high rates of morbidity, including seropositivity for HIV and Hepatitis B and C. Interventions based on risk-reduction in this population have had limited effectiveness. Recent research emphasizes that removal from the street should be a primary focus of HIV risk-reduction for homeless youths. Studies of risky behaviors in non-homeless youths and in at-risk adults strongly suggest that a better understanding of the relationships within which risk behaviors take place and of the meaning of the risky behaviors to the actors will lead to more effective interventions. The applicant is a pediatrician and specialist in adolescent medicine who has expertise in the ethnographic study of marginalized youths and experience in quantitative behavioral studies of risky behavior in adolescents. The candidate's career objective is to improve the health of marginalized youths, including homeless youths, through multidisciplinary research on the behavioral determinants of the health- related behaviors and barriers to care in this population. In the training phase of the award the applicant will have four primary development objectives: a) to develop further skills in patient-oriented qualitative research, b) to learn to follow longitudinal cohorts of hard-to-reach populations, c) to gain additional expertise in the integration of qualitative and quantitative methodologies in the study of adolescent health-related behavior, and d) to learn to analyze social network data in the study of risky behavior. She will pursue her objectives through mentored research experiences. These will be complemented by focused course work offered by the K-30 funded Advanced Training in Clinical Research program at the University of California, San Francisco. The objective of the research phase of the award will be to conduct a joint ethnographic-epidemiological-social network study to test the findings of her preliminary research. These findings, based on a street-based ethnographic study of youths, suggest that youths pass through stages of a life cycle of homelessness, each of which is characterized by different levels of acculturation to the street and different compositions of their social networks. By demonstrating in a large street-based longitudinal sample that youths in each stage differ according to acculturation and social networks and that these differences are correlated with rates of risky behaviors, we may have a powerful tool for designing interventions. An approach to intervention based on an understanding of these stages has practical implications, including new screening tools, the designing of stage- based services, and the development of intensive programs for the youths who are most susceptible to removal from the street. An understanding of how social network connections promote and prevent risky behaviors would also have significant implications for the designing of interventions with this population.